Meade LXD75 Schmidt Cassegrain

Meade's LXD75 (Plate 13) is a standard 8-inch aperture SCT optical tube mounted on an imported (Chinese) GEM. Although this model is hardly in the high-priced league, it is an attractive and fairly reliable scope whose mounting offers a surprising number of high-tech features thanks to its Autostar computer hand control.


Plate 13. (LXD 75 SCT) Meade LXD75 8-inch Schmidt Cassegrain. Credit: Image courtesy of Meade Instruments Corporation.

This mount is very similar to Japanese scope maker Vixen's renowned Great Polaris GEM, if not as sturdy or well finished. Most imported GEMs in this payload class (20 pounds) are "clones" of the Vixen. The LXD75 tube itself does not feature frills, like the mirror locks and motorized Crayford-style focusers found in the high-end Meade telescope, but the optics are the same as those used in the company's other standard SCT OTAs and come equipped with Meade's UHTC, on the primary mirror, secondary mirror, and corrector plate.

A frequent question is whether UHTC make a difference. The answer is "yes." When comparing a Meade OTA equipped with these coatings to one without, the UHTC telescope clearly shines as the winner. Images of DSOs are noticeably brighter due to the higher transmission of the UHTC corrector and the higher reflectivity of the primary and secondary mirrors. Though the difference is not overwhelming, it is there, and sometimes it makes the difference between seeing and not seeing difficult DSOs.

Mechanically, there are no surprises in store for the LXD75 owner. The moving mirror focuser is smooth and focus shift is minimal, about 45 to 60 arc seconds in the examples tested. The 75's tube is finished a gleaming white, a color that is extremely attractive and that matches the similarly finished mount. White is an unusual color for CAT tubes these days, but it may be a plus. A white finish may aid in the thermal cooldown that is necessary when an SCT is taken from a warm house and into the cold night air. The white tube may radiate heat away from the tube interior more quickly than a dark color.

The mount this tube rides on, although not fancy, is workmanlike and workable. Operationally, its German mount is more complicated for beginners to learn to use than a fork. The major difference is that, as discussed in Chapter 3, the GEM must be at least roughly polar aligned if it is to accurately go-to and track sky objects. That involves pointing the right ascension (RA) axis of the mount at the North (or South) Celestial Pole, which lies about half a degree from bright Polaris, the North Star. This polar alignment process can be somewhat confusing for a beginner but is not overly difficult since perfection is not required for most observing tasks. For visual use or casual picture taking, it is only necessary to get the RA axis pointed close to the pole, and Meade has made that fairly simple with the LXD75's polar alignment telescope (polar alignment viewfinder), which is inserted through the mount's hollow RA (polar) axis. Place Polaris on the correct spot on this small refractor's reticle using the mount head's altitude and azimuth adjusters, and the LXD75 is more than ready for go-to and visual observing.

Once the LXD75 mount is polar aligned, the user switches on the power and uses the Autostar computer to do a go-to alignment. In its most basic form, that involves entering current date, time, latitude, and longitude into the HC and centering two alignment stars. Normally, the Autostar picks a pair of stars and moves the telescope to the positions where it thinks they should be. The observer uses the hand control's direction buttons to center these stars in the finder and then in the eyepiece. Once that is done, the scope should theoretically be able to find any of the 30,000 stars, planets, and DSOs in the Autostar's memory—theoretically.

Beyond the obvious fact that at least some of those thousands of galaxies, clusters, and nebulas (the Autostar includes the entire Messier, NGC, and IC catalogs) are going to be beyond the reach of an 8-inch telescope, the LXD75 will need a careful go-to alignment to perform well. Even centering the two stars precisely with a high-power crosshair reticle eyepiece usually did not ensure good accuracy. For that, you may need to forgo the two-star "Easy Alignment" and use the more accurate "Three Star Alignment" instead. In Three Star mode, the Autostar chooses an additional alignment star on the opposite side of the sky from the other two (on the other side of the local meridian). That allows the Autostar computer to take into account any misalignment caused by less-than-perfect mechanical alignment of the mount's axes, something that is common on all but the most expensive German mounts.

Featurewise, the LXD75 hardly seems an inexpensive telescope. Thanks to the Autostar, it has more features than you can shake a Nagler eyepiece at. Not only does the HC contain a library of 30,000 objects, it provides descriptive data for many of these wonders. Center the Great Orion Nebula, press a button, and the computer scrolls a message across the display telling all about M42: how big, how far away, and more. Some of the Autostar's other capabilities, which frankly are amazing to find in an introductory telescope, include guided tours, periodic error correction (PEC) for long-exposure imaging, and computer control via a laptop. Stumped about what to look at on a given evening? Take a guided tour. The "Tonight's Best" excursion will send the LXD75 to the "best" astronomical objects visible on a given date. The Autostar contains a number of other similar expeditions, and it is even possible for the LXD75 owner to write personalized tours with the aid of a personal computer (PC).

Do you fancy taking long-exposure deep sky images? The LXD75's mount may be a little light for that demanding task, but the Autostar can help achieve success with its PEC feature. As mentioned in the discussion of mounts in Chapter 3, all gears contain slight imperfections that cause small tracking errors that spoil longexposure photos if not "guided out." PEC allows the HC button presses made to keep a star centered in a high-power crosshair eyepiece during guiding to be "recorded." The finished PEC recording can be played back for the rest of the evening, automatically making corrections. PEC is not perfect, and a guide star will still need to be closely monitored during exposures, but corrections will be fewer and smaller with PEC than without.

A telescope is more than just a mount and a tube; a few accessories are needed before any observing can be done. How does the LXD75 stack up there? It is a little Spartan but not overly so compared to other SCTs, including considerably more expensive ones. In the box, in addition to the tube, mount, and Autostar hand control, there's a 26-mm Plossl eyepiece, an imported ocular that, while not a world beater, is of decent quality. There is also a 1.25-inch format prism star diagonal that, like the eyepiece, is usable if not exactly impressive in its build quality or performance. Even though this is a go-to scope, a decent finder is needed to help locate go-to alignment stars (or objects the computer misses). Meade's 7 X 50 is a good one, providing prominent crosshairs, a wide field, and enough aperture to pull stars out of light-polluted suburban skies. Finally, there is a battery pack that holds eight D cells for powering the mount. Unfortunately, the D cells will not power the telescope for long, especially in cold weather. Forget this battery pack and purchase the optional 12-volt power cable so you can run this surprisingly power-hungry mount off a hefty 12-volt direct current battery.

How good is the LXD75 SCT? What are the negatives? There are not many. The LXD75's predecessor, the LXD55 had a poor reputation, but Meade seems to have worked most of the bugs out of the new mount. Some users have found they have needed to do some tightening and tune-up of the GEM after it has been used for a while (as with the LXD55, the declination drive gears tend to suffer from loose setscrews over time). Mostly, the mount seems reliable and fairly accurate. The LXD75 GEM is not heavy duty, of course. "Medium duty" might even be stretching it, but it is at least sufficient for the short SCT tube. The mount could use a little sound suppression. When it is slewing to an object at high speed, it sounds as if it is grinding a pound or two of coffee in the process.

What is there to like? A lot, beginning with very good 8-inch optics. Under a dark sky, this CAT is going to impress. It is more than capable of showing all the basic wonders of the universe. Brighter DSOs—like the Messiers—will display considerable detail, as will the Moon, Mars, Jupiter, and Saturn when they are well placed. No, the mount is not rock solid, but part of this scope's appeal is its light weight and the fact that it can be disassembled into mount and tube, making it easy to waltz around a dark backyard. Its eminently reasonable $1,500 price tag does not hurt, either. With its long list of features and its big library of objects, this scope could keep even a fairly demanding astronomer happy for years.

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    How to polar align meade lx90?
    1 year ago

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